After an unknown explosion at Manchester Arena on May 22, armed police officers guard around the venue in northern part of Manchester, the U.K. / AP-Yonhap

By Eom Da-sol

A couple hugs each other outside Manchester Arena in Manchester, the U.K., May 22. / AP-Yonhap

Twenty-two people, including children, were killed when a suicide bomber detonated a bomb at a concert venue in the northern British city of Manchester on Monday night.

Greater Manchester Police said a lone male attacker was responsible for the blast at the Manchester Arena that also injured 59 people.

The explosion ripped through a foyer at the venue, the biggest indoor arena in Europe, shortly after U.S. singer Ariana Grande's concert.

Thousands of concertgoers screamed as they escaped in panic.

"We were making our way out and when we were right by the door there was a massive explosion and everybody was screaming," concertgoer Catherine Macfarlane told Reuters.

U.K. Prime Minister Theresa May paid tribute to the victims and said authorities are "working to establish the full details of what is being treated by the police as an appalling terrorist attack." She also suspended all election campaigning for the June 8 general election.

Police closed Manchester's Victoria Station, the closest station to the venue.

Ariana Grande's staff tweeted that the singer is unhurt.

In July 2005, four British Muslims killed 52 people and injured over 700 people in suicide bombings on London's transport system.